Conventional poultry production uses antibiotics to prevent disease and stimulate animal growth. Over time as a group of animals is continually fed sub-therapeutic levels of antibiotics to enhance their growth, susceptible bacteria within the gastrointestinal tract of these animals will develop resistance. When these bacteria are ingested via improperly handled meat it is possible for individuals to become ill, and such individuals may not respond to treatment with antibiotics that are the same or similar to those fed to the animals. Therefore, it is recommended that antibiotics used to treat human illnesses not be administered to food animals. The World Health Organization (WHO) urges efforts to phase out antimicrobials that are used to treat humans for growth promotion in livestock (WHO Global Strategy Recommendations). Motivated by health concerns over the potential of antibiotic resistance bacteria in the food supply, environmental concerns, animal welfare and quality concerns, many consumers are seeking alternatives to conventional meat products that are typically produced with routine use of antibiotics (Allen and Stanton, 2014; Cheng et al., 2014). Accordingly, consumer demand for chicken and turkey that has been raised without the use of antibiotics is growing to the point that production of poultry raised without the routine use of antibiotics has become part of the mainstream.
Common bacterial disease challenges facing poultry that are conventionally treated with antibiotics include colibacillosis caused by Avian Pathogenic Escherichia coli (APEC), as well as enteric diseases caused by various species from the Clostridium genus.
Although Escherichia coli are normal residents of the gastrointestinal tract in poultry, some strains carry virulence genes and are able to cause colibacillosis in birds. These virulent E. coli strains, known as Avian Pathogenic Escherichia coli (APEC), are a heterogeneous group comprising a wide diversity of serotypes and containing an array of virulence genes (Guabiraba and Schouler, 2015). Collibacillosis in poultry may be localized or systemic and includes disease states such as colisepticemia, coligranuloma (Hjarre's disease), air sac disease (chronic respiratory disease, CRD), swollen-head syndrome, venereal colibacillosis and coliform cellulitis (inflammatory process), peritonitis, salpingitis, orchitis, osteomyelitis/synovitis (turkey osteomyelitis complex), panophthalmitis, omphalitis/yolk sac infection and enteritis (Barnes H J et al., 2008). Although difficult to quantify these various disease forms are responsible for significant economic losses in poultry. For instance, lesions consistent with colisepticemia were present on 43% of broiler carcasses condemned at processing. A reduction in the levels of APEC strains will reduce rates of disease and have a positive effect on the productivity of commercial broiler operations.
Necrotic enteritis, caused by C. perfringens, is the most common and severe clostridial enteric disease in poultry (Barnes H J, 2008; Cooper et al., 2013). Necrotic enteritis outbreaks are sporadic, but typically occur in broilers between 2-6 weeks of age (Cooper et al., 2013). It has been estimated that global necrotic enteritis outbreaks result in a loss of over $2 billion annually through increased medical costs, reduced weight gain and mortality amongst animals (Lee et al., 2011a; Timbermont et al., 2011). The characteristic intestinal lesions are generally considered to be caused by the production of alpha toxin by C. perfringens Type A (Al-Sheikhly and Truscott, 1977a, 1977b, 1977b) with NE toxin B (NetB) also having been implicated in disease (Keyburn et al., 2008, 2008, 2010a; Rood et al., 2016). C. perfringens is a normal resident of the intestinal tract of poultry usually at levels below 104 CFU/g intestinal contents, but found at levels about 107 CFU/g in diseased birds (Shojadoost et al., 2012). Therefore, maintaining low levels of C. perfringens can ameliorate the onset of disease. Furthermore, C. perfringens infections have been shown to increase when antibiotic growth promoters were removed from poultry feed in Scandinavian countries, and it is anticipated that the forthcoming removal of antibiotic growth promoters from poultry feed in the USA will have a similar effect (Grave et al., 2004; Immerseel et al., 2009; Kaldhusdal and Løvland, 2000).
Bacteriocins, small antimicrobial peptides produced by bacteria, are alternatives to common antibiotics in livestock production. The function of bacteriocins is to allow the producer cells to compete with other microbes in their natural environment. They generally increase membrane permeability by forming pores in membranes of target cells or inhibit cell wall synthesis thereby preventing growth of susceptible microbes. Other beneficial attributes of bacteriocins include resistance to low pH and heat and little, if any, negative effects on host cells. These bacterially produced antimicrobial peptides are very similar to those produced by the host organism itself. Cationic antimicrobial peptides, such as cathelicidins, are abundantly expressed in the mucosal epithelial cells lining the digestive, respiratory and reproductive tracts, as well as in the primary and secondary immune organs of chickens, where they play an essential role in innate defense and disease resistance (Achanta et al., 2012).
There may be concern that continual exposure of bacteria to continual, high levels of bacteriocins could result in resistance developing as it does for conventional antibiotics. This risk can be greatly reduced by the combined use of a number of bacteriocins with different mechanisms of action (Riley et al., 2012). Synergistic effects between the bacteriocins allow for lower doses and multiple spontaneous mutations will have to occur to acquire resistance to a combination of bacteriocins.
What is needed are bacterial strains and combinations of bacterial strains that are bacteriocin producing as to be useful in poultry and other animals. Methods of making and using bacteriocin producing bacterial strains and combinations thereof are also needed. Additionally, methods of identifying bacteriocin producing bacterial strains that are useful in poultry and other animals are also needed.